Prepare the butter: Melt butter slowly over low heat in a small saucepan. Don't allow it to brown. Skim any milk solids from the surface. Keep warm but not hot.

Blend the yolks: Place egg yolks and lemon juice in a blender. Blend on medium speed for 30-60 seconds until the mixture is pale yellow and slightly thickened.

Add the butter: With the blender running on low speed, slowly drizzle in the hot melted butter in a thin, steady stream. This should take about 1-2 minutes. Don't add too quickly or the sauce may break.

Season: Continue blending for 30 more seconds after all butter is added. Add salt and white pepper or cayenne. Blend to combine.

Adjust consistency: If the sauce is too thick, blend in warm water, 1 tablespoon at a time, until desired consistency is reached. The sauce should coat the back of a spoon.

Taste and adjust: Taste and add more lemon juice or salt as needed. The sauce should be well-seasoned with bright acidity balancing the richness.

Keep warm: Transfer to a warm bowl and cover. Keep warm over (not in) a pan of warm water for up to 1 hour. Stir occasionally to prevent a skin from forming.

To reheat: If the sauce cools too much, place the bowl over warm (not hot) water and whisk gently until warmed through. Add small amounts of warm water if needed to restore consistency.

Serve immediately over eggs benedict, asparagus, fish, chicken, or vegetables. Store refrigerated leftovers for up to 2 days and reheat gently.